Plastometer and method



Jan. 3l, 1956 E. F. LlNHoRsT PLASTOMETER AND METHOD Filed March 2l, 1952 IN V EN TOR.

tUrJ L LPUUHTLU .A .TT ORNEY United States Patent O `2,732,701; PLAsToMETER AND METHOD Erwin F. Linhorst, Fort Wayne, Ind., assigner to United States Rubber Company, a corporation of New Jersey Application March l21, 1952, Serial No. 277,779 v2 Claims. (Cl. 73--15.6)

This invention relates to a method and apparatus for determining the plastic flow characteristics of plastics such as rubber-containing compositions under certain conditions ofpressure and temperature. In particular, the invention relates to a method and apparatus for control testing ofrubber stock to determine whether a particular batch of stock has the proper plastic characteristic which will allow it to be properly molded, injected, extruded, or compounded.

The apparatus of the present invention is of the socalled pressure type plastometer in which a test sample' of standard dimension is pressed between flat parallel platens under standard conditions of pressure and temperature and the change in thickness ofthe test sample with respect to time is recorded. Plastometers of this type heretofore available were quite bulky, complicated and expensive. It is therefore one object of the invention to provide a pressure type plastometer which is of simple and inexpensive construction, is light in weight, and which may be easily maintained, repaired and calibrated, but which at the same time will give reliable data. To this end, the apparatus is fabricated from readily available standard materials and equipment. The pressure applicating mechanism has only one moving part which is actuated by simple springs. The heating mechanism is of a simple heated liquid bath which utilizes a standard heating means and thermostat.

The method of the present invention has for one of its objects the provision of a test procedure which will give complete data on the plastic characteristics of a particular stock through a range of increasing temperatures. To this end, the heating of the test sample and the application of the standard pressure are performed substantially simultaneously. Heretofore, it was deemedlnecessary to pre-heat the sample to 100"l C. before the application of the pressure in order to get reliable data, with the result that no data couldbe-obtained on the Aplastic characteristics ofthe sample at'the interim temperatures.v By the present invention, -a measure of; the.: percentage of cure of the particular batch of stock canbe obtained, asthe method gives data on the plastic characteristic of the' stock over a range of temperatures. This method therefore eliminates the pre-heating of the sample, a necessarily time consuming operation.

Other objects and advantages of the present invention will become apparent from. the following 4description when' read in conjunction with the accompanying drawing,

wherein: A

Fig. 1 is an elevational view of the pressure application mechanism,

Fig. 2 is an isometric view of a sample to be tested and the emery paper disks between which it is sandwiched,

Fig. 3 is a partial elevational view of the pressure applicating mechanism showing how the sample and emergy disks are placed between the platens of the pressure ap-A plicating mechanism,

Fig. 4.is a sectional view taken on the line :5-5 of- 2,732,708 Patented Jan. 31, 1956 Fig. l showing the arrangement of the springs in the applicating mechanism, and

Fig. 5 is a sectional view of the complete apparatus as used in making comparative tests on test samples.

Referring to the drawing and in particular to Fig. l

- of the drawing, the apparatus of the present invention includes a pressure applicating mechanism, generally desafter. The second plate 16, which is parallel to plate 13,

is secured to the end of rod adjacent one end thereof and is secured tovrod 14 adjacent the opposite edge.

A third plate or bar,17, parallel to plates 13, and 16,' and positioned at a point intermediate the plates 13 and l 16 extends between the rods 14 and 15 and is rigid1y3secured thereto. The platen 12 is rigidly secured to one end of a rod 18 by a set screw 12a. Rod 18 is slidably mounted for axial movement towards and away from the platen 11 in aligned cylindrical holes 19 and 20 provided v respectively in plates 13 and 16 to thereby allow platen 12 to be movedtowards platen 11 to press a test sample therebetween.

Rod 18 is provided with a cross bar 21 which is freely mounted thereon and which rests on a cotter pin 21a j which extends through the rod 18 adjacent the upper end thereof but below the plate 16. Extension springs 21 and 22 are secured to the cross bar 21 adjacent opposite ends thereof by means of screw eyes 23 and 24 which are threaded into the cross bar 21. The opposite ends of the springs are connected .to headed pins 17a secured in opposite edges of the platev or bar 17 as shown in Fig. 4. Springs 21 and 22, therefore, normally urge rod 18 and platen 12 secured thereto towards platen 11 to press a test sample therebetween.v The tension in springs 23 and 24 may be adjusted as desired by shortening or lengthening the eiective length of the screw eyes 23 and 24 by varying the amount they are threaded into the cross bar 21.

A pin 25 extends through and is secured to the rod 18 above the cross bar 21. Pin 25 provides means which may be easily grasped by the iingers of the operator to "move the rod 18 upwardly against the tension of the springs so that a test sample may be removed or placed between the platens 11 and 12.

A dial indicator gauge 26, of the type well known in theart, is secured to the rod 14 adjacent the upper end thereof which extends above the plate 16. The actuating plunger 27 of the dial indicator 26 extends downwardly in axial alignment with and is contacted by the end of the rod 18 which is made suiciently long for this purpose.

it can be readily seen therefore, that the dial indicator v gauge 26 will indicate the relative thickness of a test sample placed between the platens 11 and 12 and that any change in the thickness of the sample will be reected in the reading. of the indicator dial. y v

The heatingV apparatus is shown in Fig. l and is generally designated-as 28. This apparatus includes a vacuum type insulated jar 29, generally referred to in the art as a Dewar jar. This jar is enclosed in a protective steel casing 30 which may be easily fabricated from a section of pipe. This jar is filled with an inert liquid 31 such as glycerol. A thin layer of silicone oil may be oated on the top of the glycerol to slow down the rate of evaporation of the glycerol. An annular downwardly sloping drain ring 30a is secured to the interior wall of the casing 30 above the jar 29, so that any of the liquid `31 which drains'off the pressure applicatiug mechanism it as it is removed from the jar 29 will ilow back into the jar 29.

An electrical resistance rod type heating unit 32 is secured to the inner wall o' the casing 39 and extends into the liquid. A pilot light 32a is provided to indicate when a current is ilowing through the heating unit 32. A thermostat 33 which also extends into the liquid and which is connected electrically with the heating unit, maintains the liquid at; a predetermined standard temperature. A thermometer 3d is provided to allow for easy visual check of the temperature of the liquid. The heating unit 32, thermostat 33 and the thermometer 34 are commercial items well known in the art.

An upright standard 35 is secured to the wall of the casing 30 and extends upwardly therefrom. An arm 36 is secured to the top of the standard and extends over the liquid bath. In using the invention, the pressure applicating mechanism l is suspended in the liquid bath from the arm 36 by means of a chain 37 which is attached to the end of the arm 36 by a snap hook 37a and at the other end to a hook 38 secured to the rod 14.

Referring to Fig. 2, the test sample 39 which is in the form of a thin disk is sandwiched between two disks 4t) and 41 of non-slippery thin material of uniform thickness to prevent slippage of the sample 39 from between the platens, especially when the apparatus 10 is immersed in the bath. Emery paper and ordinary kraft paper has been found to be satisfactory for this purpose. When emery paper is used, the abrasive side is placed against the sample.

In utilizing the apparatus in control testing, it is at iirst necessary to select by experiment a sample of rubber which meets the plastic characteristic requirement for the particular operation for which it is desired to be used. This is done by actually molding, extruding, injecting or compounding a number of samples of a plurality of batches of stock. Once the type of rubber which meets the requirements for the particular operation is selected, a sample of this rubber is tested in the apparatus 'in the manner as will hereinafter be described. The data se cured from testing this sample s then used as a standard by which all batches of rubber can be compared by making similar tests thereon to determine whether they are suitable for the particular molding, extruding, injecting or compounding operation. Thus, once the standard is selected, it is not necessary to again experimentally determine by actually carrying out the operation whether a particular batch of stock will be satisfactory for a particular operation.

In order to obtain comparable data, it is of course necessary that the test sample dimensions, the dimensions of the platens, the force appliedl to the sample, the temperature of the liquid, the time atV which readings arc to be taken, and the general procedure must be standardized.

I have found that the following standards give very reliable data:

Diameter of test sample, %G inch.

Thickness of test sample, 0.09.

Diameter of emery paper disk, 5A;

Grade and type of emery paper, 40G-waterproof. Diameter of platen, 1/2

Temperature of glycerol bath, '250 F.

Force applied to platens, 8 lbs. Time after which final reading made, l2 minutes.

ple 39 is sandwiched between them Awith the abrasivel side of the paper against the sample. This sandwich is then placed between the platens 11 and 12, the platen 12 being raised by means 0f pin 25. The sandwich consist ing of the sample 39 and emery paper disks 40 and 41 is placed on the platen 11 concentric therewith as shown in Fi g. 3.

it should bc noted that the sample is made slightly larger in diameter than the platens 11 and 12. This is to insure that the sample will receive a uniform pressure throughout the test. It the sample were smaller than the platens, the pressure per square inch would gradually decrease as the area of the sample increases as it was flattened out.

The tension in the springs 21 and 22 are adjusted to give eight pounds pressure. The small change in the force applied by the springs in the movement of the platen through a distance of much less than 0.1 inch is negligible and need not be considered. The platen 12 is released so that the sample is compressed between the platen 12 and the platen 1.1 and simultaneously therewith the instrument is immersed in the glycerol bath which has been previously brought to a temperature of 250 F. lt is to be understood that this temperature of 250 F. has been selected as one that will give reliable data Within a reasonable length of time but that other standard temperatures falling within the range of from 200 to 300 F. could be used for most types of rubber. For sponge rubber room temperature can be used. After twelve minutes a reading of the dial indicator is made. The reading of the dial indictor will give the thickness of the sample at this time. This thickness in mils is taken as the value which is to be compared with the standard.

it rea-dings of the thickness of the sample are taken at spaced intervals of time up to the twelve minute total, the readings will given an indication of the percentage cure of the stock, assuming curing agents are present in the stock. lf the stock tested is fairly well cured when the test is made, then the readings will be of fairly constant value. lf the stock is essentially uncured, the value ot' the thickness will decrease rather rapidly at i rst and then gradually becomes constant. As the sample cures due to the heat of the bath, the length of time that it takes for the readings of thickness to become fairly constant will be a measure of the percentage cure of the batch of stock from which the test sample was taken.

From the above description` it can be seen that there is provided a simplified method and apparatus for dctermining the plastic characteristics of a rubber-containing composition. The apparatus can bc easily constructed from readily available material and equipment. The apparatus is easily calibrated, maintained and operated. The method eliminates necessity of the time consuming. pre-heating of the test sample and at the same time gives` reliable data and also provides for the obtaining ot' data from which a measure of the percentage of cure of thc batch before testing may be determined.

It is to be understood that the above description and accompanying drawing is for the purpose of illustration only and not by Way of limitation and that changes o1 modifications may be made therein without departing from the spirit and the scope of the invention.

Having thus described my invention, what i claim and desire to protect by Letters Patent is:

l. A plastometer comprising, a pair of spaced, parallel elongated side members, a first plate extending between and secured tosaid side members adjacent the lower ends thereof, a second plate extending between and secured to said side members adjacent the upper ends thereof, a flat, circular platen secured to the upper face of said first plate, a bar secured to and extending between said side members at a point adjacent to but spaced from sai/.l first plate, said second plate and said bar having openings therethrough which are in alignment with said platen, an elongated rod Vslidably mounted in said openings fox movement towards and away from said platen, a second flat circular platen secured to the lower end of said rod, a

cross bar secured to said rod adjacent to but spaced from the upper end thereof, a pair of screw eyes adjustably threaded one in each end of said cross bar, a pair of extension springs connected at one of their ends to said bar and at their other ends to said screw eyes whereby said second mentioned platen secured to the lower end of said rod is normally urged against said rst mentioned platen to press a test sample therebetween, one of said side members extending above said second plate a substantial distance, a dial indicator secured to the extending portion of said one of said side members and having an actuating plunger in contact with the upper end of said rod whereby the thickness of the test sample placed between said platens will be indicated on said dial indicator, and a pin secured to and extending from said rod adjacent the upper end thereof to facilitate raising of the rod against the tension of said springs to permit insertion of a test sample between said platens.

2. A method of determining the plastic characteristics of a curable rubber-containing composition comprising, placing a sample of said rubber containing composition of uniform thickness between two opposed flat parallel platens of equal area slightly less than the area of said sample, compressing said sample between said platens under a constant pressure, simultaneously therewith immersing said sample in a heated bath maintained at a constant predetermined temperature of between 200 and 300 F. to cure said sample, retaining said sample while it is being compressed in said bath a suiiicient period to allow it to become substantially cured, measuring the thickness of said sample at a plurality of intervals of time and measuring said intervals of time.

References Cited in the tile of this patent UNITED STATES PATENTS 989,471 Abraham Apr. 11, 1911 1,037,596 Coppage Sept. 3, 1912 1,184,837 Edgecomb May 30, 1916 1,952,523 Abbott Mar. 27, 1934 2,066,016 Rossi et al Dec. 29, 1936 2,222,470 Barnes Nov. 19, 1940 2,479,984 Stock Aug. 23, 1949 2,482,147 Bashore Sept. 20, 1949 

1. A PLASTOMETER COMPRISING, A PAIR OF SPACED, PARALLEL ELONGATED SIDE MEMBERS, A FIRST PLATE EXTENDING BETWEEN AND SECURED TO SAID SIDE MEMBERS ADJACENT THE LOWER ENDS THEREOF, A SECOND PLATE EXTENDING BETWEEN AND SECURED TO SAID SIDE MEMBERS ADJACENT THE UPPER ENDS THEREOF, A FLAT, CIRCULAR PLATEN SECURED TO THE UPPER FACE OF SAID FIRST PLATE, A BAR SECURED TO AND EXTENDING BETWEEN SAID SIDE MEMBERS AT A POINT ADJACENT TO BUT SPACED FROM SAID FIRST PLATE, SAID SECOND PLATE AND SAID BAR HAVING OPENINGS THERETHROUGH WHICH ARE IN ALIGNMENT WITH SAID PLATEN, AN ELONGATED ROD SLIDABLY MOUNTED IN SAID OPENINGS FOR MOVEMENT TOWARDS AND AWAY FROM SAID PLATEN, A SECOND FLAT CIRCULAR PLATEN SECURED TO THE LOWER END OF SAID ROD, A CROSS BAR SECURED TO SAID ROD ADJACENT TO BUT SPACED FROM THE UPPER END THEREOF, A PAIR OF SCREQ EYES ADJUSTABLY THREADED ONE IN EACH END OF SAID CROSS BAR, A PAIR OF EXTENSION SPRINGS CONNECTED AT ONE OF THEIR ENDS TO SAID BAR AND AT THEIR OTHER ENDS TO SAID SCREW EYES WHEREBY SAID SECOND MENTIONED PLATEN SECURED TO THE LOWER END OF SAID ROD IS NORMALLY URGED AGAINST SAID FIRST MENTIONED PLATEN TO PRESS A TEST SAMPLE THEREBETWEEN, ONE OF SAID SIDE MEMBERS EXTENDING ABOVE SAID SECOND PLATE A SUBSTANTIAL DISTANCE, A DIAL INDICATOR SECURED TO THE EXTENDING PORTION OF SAID ONE OF SAID SIDE MEMBERS AND HAVING AN ACTUATING PLUNGER IN CONTACT WITH THE UPPER END OF SAID ROD WHEREBY THE THICKNESS OF THE TEST SAMPLE PLACED BETWEEN SAID PLATENS WILL BE INDICATED ON SAID DIAL INDICATOR, AND A PIN SECURED TO AND EXTENDING FROM SAID ROD ADJACENT THE UPPER END THEREOF TO FACILITATE RAISING OF THE ROD AGAINST THE TENSION OF SAID SPRINGS TO PERMIT INSERTION OF A TEST SAMPLE BETWEEN SAID PLATENS. 